This application is the U.S. national-phase application of PCT International Application NO. PCT/JP96/03582.
The present invention relates to a catalytic combustion apparatus superior in characteristics of an exhaust gas for catalytically combusting a gaseous fuel or liquid fuel that is vaporized, and utilizing the combustion heat and exhaust gas for such applications as heating, air heating and drying.
Conventionally, a catalytic combustion apparatus for catalytically combusting a gaseous or liquid fuel for heating, air heating and drying has been generally constituted as shown in FIG. 9.
By using FIG. 9, the constitution is described. In FIG. 9, a fuel gas supplied from a fuel supply valve 1 is mixed in a premixing chamber 3 with air supplied from an air supply valve 2, and sent to a preheating burner 4 as a premixed gas. It is ignited by an ignition device 5, and forms a flame at the preheating burner 4. An exhaust gas of a high temperature caused by the flame heats a catalytic element 7 provided in a combustion chamber, passes there through, and is discharged from an outlet 8. When the catalytic element 7 is heated to a temperature at which it is active, supply of the fuel is temporarily discontinued by the fuel supply valve 1, and the flame is distinguished. By restarting supply of the fuel immediately after that, catalytic combustion is initiated. The catalytic element reaches a high temperature, and emits heat radiantly through a glass 9 that is located in a position opposite to an upstream surface of the catalytic element as well as in the form of a hot exhaust gas from the outlet 8 for heating and air heating applications.
Because the catalytic combustion is surface combustion, a large quantity of radiation is emitted from the catalytic element in correspondence with a temperature of the catalytic element and an apparent surface area of the catalytic element. In a catalytic combustion apparatus for heating and air heating by means of heat exchange using a heating medium, combustion heat generated on the catalytic element must be efficiently exchanged with the heating medium. It is, therefore, required that a radiation from a surface of the catalytic element is effectively exchanged. However, it has been a problem that an efficiency of heat exchange of a catalytic combustion apparatus is reduced correspondingly, if heat radiated from the catalytic element, instead of being conducted to a heat exchanger, is applied to, other outer wall of the combustion apparatus, or emitted outside the combustion apparatus.
Thus, in order to solve the problem, the invention intends to realize a catalytic combustion apparatus effectively utilizing a radiation from a surface of catalytic element for providing a high efficiency of heat exchange.
Further, in the case a catalytic element is employed in a combustion chamber, combustion heat on the catalytic element is conducted by thermal conduction to the combustion chamber from an attachment part to the combustion chamber.
Therefore, it has been a problem that the catalytic element is lower in temperature in the vicinity of a catalytic element holder, the catalytic activity is locally reduced, and an exhaust gas containing unburned combustibles is emitted.
Hence, it is an object of the invention to prevent emission of unburned combustibles from an attachment part of catalytic element to a combustion chamber, and provide a catalytic combustion apparatus superior in characteristics of an exhaust gas.
In addition, in the case sensible heat of a combustion gas is exchanged by means of such heat exchanger as a fin-tube type, when the heat exchanger is placed above a catalytic element, because combustion heat is used for raising the temperature of the combustion apparatus itself at the time of startup of the combustion apparatus, and the temperature of an exhaust gas cannot be very high, condensation is caused on the heat exchanger, and the catalytic element may be wetted. If the catalytic element is wetted by the condensed water, the temperature is reduced, the catalytic activity is lowered, and the reactivity may be locally reduced. Also, as condensation on the heat exchanger should not be allowed, positive heat exchange was unachievable, and it was forced that the latent heat in the combustion gas be discharged as an exhaust loss instead of being collected.
Thus, in order to solve the problem, the invention intends to prevent combustion characteristics from being locally affected by condensed water, and allow stable combustion to be maintained by providing a heat exchanger above a heat exchanger, and discharging water condensed on the heat exchanger to outside a combustion apparatus. The invention also intends to realize a catalytic combustion apparatus providing a very high efficiency of heat exchange by collecting latent heat in a combustion gas at the same time.
The invention provides, as defined in claim 1, a catalytic combustion apparatus comprising a fuel supply member for supplying a fuel, an air supply member for supplying combustion air, a premixing chamber for mixing the fuel supplied from the fuel supply member and the air supplied from the air supply member to make a mixed gas, a catalytic element in the shape of a plate consisting of a porous member for catalytically combusting the mixed gas and a combustion chamber provided in a downstream side of the premixing chamber, containing the catalytic element in the shape of a plate, and incorporating a first radiated heat receiving member that is positioned opposite to either one of two surfaces of the catalytic element as a part of its side wall.
The first radiated heat receiving member may have a heating medium channel tightly adhered thereto or incorporated therein.
The combustion chamber may incorporate a second radiated heat receiving member that is positioned opposite to the other of two surfaces of the catalytic element as a part of its side wall.
The second radiated heat receiving member may have a heating medium channel tightly adhered thereto or incorporated therein.
In an outlet of the combustion chamber, a second catalytic element in the shape of a plate consisting of a porous member may be provided.
A radiation absorbing layer may be employed in a surface of the first radiated heat receiving member inside the combustion chamber.
A radiation absorbing layer may be provided in a surface of the second radiated heat receiving member inside the combustion chamber.
The catalytic combustion apparatus further comprises a heat exchanging member provided in a downstream side of the combustion chamber, wherein the combustion chamber may be located above the heat exchanging member.
The invention provides, as defined in claim 9, a catalytic combustion apparatus comprising a catalytic element with multiple through-holes for combusting a mixed gas of a fuel and air, a combustion chamber containing the catalytic element, and having a radiated heat receiving member that is positioned opposite to an upstream side of the catalytic element in the flowing direction of the mixed gas, a first heating medium channel provided in the radiated heat receiving plate, a second heating medium channel located downstream of the catalytic element in the flowing direction, and having multiple fins and an exhaust path formed between the fins, wherein the multiple fins are placed at least in a position opposite to either end of the catalytic element.
According to such constitution, by reducing a spacing between the fins, and increasing a length in the flowing direction, for example, radiation from a downstream surface of the heating medium is almost fully directed to the fins and the second heating medium channel.
Now, operation of the invention is described below by way of example.
Generally, in a catalytic combustion apparatus, combustion is conducted in such condition that an upstream portion of catalytic element is at the highest temperature, and a large quantity of heat radiated from the upstream surface at the high temperature of catalytic element is made use of.
Thus, by using a catalytic element in the shape of a plate that provides a large apparent surface area, and employing a radiated heat receiving member in a position opposite to the catalytic element, the large quantity of heat radiation conducted from the surface of catalytic element can be received by the radiated heat receiving member. Since the radiated heat receiving member receiving the heat has a channel for passing a heating medium tightly adhered thereto or incorporated therein, the heat is conducted to the channel for passing the heating medium, and further exchanged with the heating medium in the channel.
Now, because the heat is conducted to the radiated heat receiving member by radiative conduction, the heat is evenly removed from the entire catalytic element. Therefore, since unevenness in temperature caused as the combustion heat is removed by direct thermal conduction from a part of the catalytic element is prevented, the large quantity of combustion heat on the catalytic element can be transferred to the heating medium, while stable combustion is maintained. In addition, because the temperature of upstream surface of the catalytic element that is at the highest temperature is reduced by positive heat exchange with the radiated heat receiving member, a higher combustion capacity can be achieved without increasing the temperature of catalytic element to a limit of its heat resistance. As a result, a compact catalytic combustion apparatus using a heating medium for heat exchange can be realized.
Further, by providing the first and second radiated heat receiving members in opposition to respective surfaces of the plate-like catalytic element, because radiation from both surfaces of the catalytic element can be captured by the first and second radiated heat receiving members for heat exchange, and outer surfaces of the catalytic element are simultaneously formed by the first and second radiated heat receiving members, outer surfaces of the catalytic combustion apparatus can be maintained at a low temperature. As a result, radiation loss due to removal of heat by natural convection and radiation from the outer surfaces of catalytic combustion apparatus can be reduced, and an efficiency of heat exchange can be increased.
As heat is removed from the catalytic element to the second radiated heat receiving member, because the temperature of catalytic element is reduced in the opposite side thereof, and the temperature of catalytic element in a side opposite to the first radiated heat receiving member is also reduced due to thermal conduction within the catalytic element, the combustion capacity is further increased. Therefore, a catalytic combustion apparatus providing a high efficiency of heat exchange can be realized in a more compact size.
By providing the second catalytic element in a downstream side of the combustion chamber, since heat radiation from the second catalytic element can be also received by the radiated heat receiving member, an efficiency of heat exchange in the catalytic combustion apparatus can be further increased. Simultaneously, a small quantity of unburned combustibles discharged from the first catalytic element is combusted, and a catalytic combustion apparatus superior in characteristics of an exhaust gas can be achieved.
Further, by providing a radiation absorbing layer in a surface of the radiated heat receiving member, since radiation from a surface of the catalytic element can be very efficiently received by the radiated heat receiving member, an efficiency of heat exchange can be further increased.
By placing the catalytic element above a heat exchanging member for collecting sensible heat in a combustion gas that is produced in the catalytic element, even if condensation of water is caused on the heat exchanging member due to any condition, the water condensed is discharged to outside the combustion apparatus, moving downward from the heat exchanging member in the discharging direction of exhaust gas.
Thus, combusting conditions cannot be affected due to wetting of the catalytic element, and stable combustion can be maintained. Now, although the pH value of water condensed is at 3 or a lower value in the case of inflaming combustion, because NOx is contained in a combustion gas, almost no NOx is contained in the case of catalytic combustion, and no other substance is, therefore, contained in the water condensed except such soluble contents as CO2 and H2O in a combustion gas. Thus, the pH value is at 6, and corrosion of the heat exchanger by the water condensed can be prevented.
Accordingly, as latent heat in a combustion gas can be collected by positive heat exchange, a catalytic combustion apparatus very high in efficiency of heat exchange can be realized.